The contribution of remotely sensed ENA observations from the Interstellar Boundary Explorer (IBEX; [1]}) and particularly the Cassini/Ion and Neutral Camera (INCA; [2]}) that covers the \(>\) 5.2 to \(\sim \) 28 keV part of the PUI distribution that is not measured in-situ by the Voyagers, was unequaled (see also Section ). These observations further corroborate the complexity of the \(\sim \) 10 eV to \(\sim \) 344 MeV energy spectra inside the IHS [3]}, revealing a number of softening and/or hardening breaks that possibly correspond to acceleration mechanisms inside the IHS that are not currently described by sophisticated recent models [4]}. A recent model from [5]} showed that a proton distribution that is consistent with the IBEX measurements, requires a ten times higher turbulence power ratio at the TS that that observed by Voyager [6]}. Overall, the shape of the ion energy spectra plays a critical role toward determining the ion energetics, the acceleration mechanisms and the possible sources of different plasma and suprathermal ion populations.
